|  | 2.3 | Switching and VLANs
| 2.3.9 | Two switching methods

Two switching modes can be used to forward a frame through a switch: Store-and-forward-The entire frame is received before any forwarding takes place. The destination and/or the source addresses are read and filters are applied before the frame is forwarded. Latency occurs while the frame is being received; the latency is greater with larger frames because the entire frame takes longer to read. Error detection is high because of the time available to the switch to check for errors while waiting for the entire frame to be received. Cut-through-The switch reads the destination address before receiving the entire frame. The frame is then forwarded before the entire frame arrives. This mode decreases the latency of the transmission and has poor LAN Switching error detection. Fast-forward and fragment-free are two forms of cut-through switching: Fast-forward switching-Fast-forward switching offers the lowest level of latency by immediately forwarding a packet after receiving the destination address. Because fast-forward switching starts forwarding before the entire packet is received, there may be times when packets are relayed with errors. Although this occurs infrequently and the destination network adapter discards the faulty packet upon receipt, the superfluous traffic may be deemed unacceptable in certain environments. Use the fragment-free option to reduce the number of packets forwarded with errors. In fast-forward mode, latency is measured from the first bit received to the first bit transmitted, or first in, first out (FIFO). Fragment-free switching-Fragment-free switching filters out collision fragments, which are the majority of packet errors, before forwarding begins. In a properly functioning network, collision fragments must be smaller than 64 bytes. Anything greater than 64 bytes is a valid packet and is usually received without error. Fragment-free switching waits until the received packet has been determined not to be a collision fragment before forwarding the packet. In fragment-free mode, latency is measured as FIFO. The latency of each switching mode depends on how the switch forwards the frames. The faster the switching mode, the smaller the latency in the switch. To accomplish faster frame forwarding, the switch takes less time to check for errors. The tradeoff is less error checking, which can lead to a higher number of retransmissions.
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